Tried searching but did not (yet) find this discussed. Anyone have a solution or clues as to what's going on? The wife mentioned this happening to her yesterday (she rarely drives the Prius) and I had it happen twice today as well... Just a minor bump at 60-70mph and without warning the car would slow down. I haven't observed the skiddinglight flashing when it happened, but I can imagine that might be the cause (summer tires in 2-5 C temperatures (~35-40F) and wet conditions). Pushing the 'restore' or whatchamacallit button (push stalk upwards) would let it accelerate to the old set speed, so it is not 'forgetting' its settings, just 'releasing' the cruise control.